Some of my students have been struggling to create pdf documents from rhino. The usual reason is that they lack of the basic drivers for printing. Creating 2D PDF drawings requires a PDF printer driver. Some drivers cost money. Some are free. A list of drivers available here:

When printing a 2D PDF you need to determine which style you would like to print. You can choose between a vector style PDF file and a raster type PDF file. Vector PDFs have the advantage in printing to larger paper sizes and getting sharp linework at any size. Raster PDFs will handle images and shaded modes coming from Rhino, but limit the sharpness of the print based on a preset resolution of the PDF. See details below on 2D PDF.